The enteric nervous system (ENS) is formed by cells that migrate from the neural crest. Once they reach the gut their differentiation is influenced by signals from the microenvironment, specifically, the extracellular matrix (ECM). Studies have shown that crest-derived cells express a receptor (LBPI 10) when they enter the bowel. The expression of this receptor is a mark of differentiation. In the ls/ls mouse the terminal colon is aganglionic and extracellular matrix molecules including laminin are overexpressed in the colon. The investigators believe that the over- expression of laminin- 1 blocks the migration and differentiation of crest-derived cells in the ls/ls colon and therefore leads to aganglionosis. Recent studies have shown that aganglionosis of the colon occurs when endothelin-3 (EDN3) or endothelin-B receptors (EDNRB) are deficient and the ls/ls mouse does not produce endothelin-3. They propose to test the following hypotheses: 1) that EDN3 interacts with smooth muscle or interstitial cells (ICCs) and down regulates their secretion of laminin and other ECM molecules; 2) that a deficiency of EDN3 leads to an overexpression of laminin- 1 and; 3) that the overexpression of laminin- l causes the crest-derived cells to differentiate prematurely and therefore are unable to colonize the bowel. Their first studies propose to answer the question, does interaction of EDN3 with the endothelial receptor modulate the biosynthesis of laminin-I in the mesenchyme of fetal colon and pelvis? They have developed a method of immunoselection that allows them to separate and isolate crest-derived and non-crest- derived cells from the mesenchyme of fetal bowel. They propose to isolate these cells and culture them in defined media and determine their response to EDN3. They hope to show that EDN3 downregulates expression of laminin- l in control mice and that upregulation of these molecules occurs when EDN3 or EDNRB are deficient. Their second set of experiments will attempt to identify the cells that are responsible for expression of ECM molecules in the colon of ls/ls mice. They will use immunocytochemistry to identify these cells. They also will use a drug called brefeldin A which blocks secretion of proteins and should enhance the identification of the cells. In their third series of studies they will determine whether the overexpression of laminin- 1 in the ls/ls mouse blocks the migration of crest-derived cells. They will perform these studies by adding a peptide called IKVAV which blocks the effects of laminin on crest-derived cells and determine if this peptide can reverse the defect in ls/ls mice. Lastly, they propose to determine why the defect in the ls/ls mouse is colon specific. They propose this occurs because EDNRBs and EDN3 expression occurs only in the colon and not the small intestine. Therefore, they will compare the expression of EDN3 and EDNRB in the colon and small intestine to see if this is correct.